:root {
  --bg: #f7f5f0;
  --surface: #ffffff;
  --text: #1c1c28;
  --muted: #6e6e82;
  --border: #e2dfd6;
  --accent: #2c4a6e;
  --gain: #1b6b45;
  --loss: #a12828;
  --shadow: 0 8px 32px rgba(28, 28, 40, 0.08);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Segoe UI", system-ui, sans-serif;
  line-height: 1.5;
}

.app {
  max-width: 640px;
  margin: 0 auto;
  padding: 1rem 1.25rem 1rem;
  min-height: 100svh;
  display: flex;
  flex-direction: column;
}

.home-link {
  align-self: flex-start;
  margin: 0 0 1.25rem;
  color: var(--muted);
  font-size: 0.82rem;
  font-weight: 600;
  text-decoration: none;
}

.home-link:hover {
  color: var(--accent);
}

header {
  text-align: center;
  margin-bottom: 2.5rem;
}

header h1 {
  margin: 0;
  font-size: 1.5rem;
  font-weight: 600;
  letter-spacing: -0.02em;
}

header p {
  margin: 0.35rem 0 0;
  color: var(--muted);
  font-size: 1rem;
}

.matchup {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: end;
  gap: 0.75rem;
}

.swap-btn {
  align-self: center;
  margin-bottom: 1.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 2.75rem;
  height: 2.75rem;
  padding: 0;
  border: 2px solid var(--border);
  border-radius: 50%;
  background: var(--surface);
  color: var(--muted);
  font-size: 1.25rem;
  line-height: 1;
  cursor: pointer;
  box-shadow: var(--shadow);
  transition: border-color 0.15s, color 0.15s, transform 0.15s;
}

.swap-btn:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.swap-btn:active {
  transform: scale(0.94);
}

.swap-btn:focus-visible {
  outline: none;
  box-shadow: 0 0 0 4px rgba(44, 74, 110, 0.12), var(--shadow);
}

.rating-field {
  display: grid;
  gap: 0.5rem;
}

.rating-field span {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.rating-field input {
  width: 100%;
  font: inherit;
  font-size: 2.25rem;
  font-weight: 600;
  text-align: center;
  padding: 1rem 0.5rem;
  border: 2px solid var(--border);
  border-radius: 16px;
  background: var(--surface);
  color: var(--text);
  box-shadow: var(--shadow);
  transition: border-color 0.15s, box-shadow 0.15s;
  -moz-appearance: textfield;
}

.rating-field input::-webkit-outer-spin-button,
.rating-field input::-webkit-inner-spin-button {
  -webkit-appearance: none;
  margin: 0;
}

.rating-field input::placeholder {
  color: #c8c4bb;
  font-weight: 500;
}

.rating-field input:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 4px rgba(44, 74, 110, 0.12), var(--shadow);
}

.advanced-toggle {
  margin: 1.25rem auto 0;
  padding: 0;
  border: none;
  background: none;
  color: var(--muted);
  font: inherit;
  font-size: 0.8rem;
  cursor: pointer;
  text-decoration: underline;
  text-underline-offset: 3px;
}

.advanced-toggle:hover {
  color: var(--text);
}

.advanced[hidden] {
  display: none;
}

.advanced:not([hidden]) {
  display: grid;
  gap: 1rem;
}

.advanced {
  margin-top: 0.75rem;
  padding: 1rem 1.25rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
}

.advanced-explain h2,
.advanced-explain h3 {
  margin: 0 0 0.5rem;
  font-size: 0.95rem;
  font-weight: 600;
}

.advanced-explain h3 {
  margin-top: 1rem;
  font-size: 0.9rem;
}

.advanced-explain a {
  color: var(--accent);
}

.advanced-explain p {
  margin: 0 0 0.65rem;
  font-size: 0.88rem;
  color: var(--muted);
  line-height: 1.55;
}

.advanced-explain p:last-child {
  margin-bottom: 0;
}

.advanced-explain strong {
  color: var(--text);
  font-weight: 600;
}

.advanced-explain ul {
  margin: 0 0 0.65rem;
  padding-left: 1.2rem;
  font-size: 0.88rem;
  color: var(--muted);
  line-height: 1.55;
}

.advanced-explain li + li {
  margin-top: 0.35rem;
}

.formula {
  padding: 0.55rem 0.75rem;
  background: var(--bg);
  border-radius: 8px;
  font-family: ui-monospace, Consolas, monospace;
  font-size: 0.82rem !important;
  color: var(--text) !important;
  text-align: center;
}

.k-factor-row,
.advanced label {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  font-size: 0.9rem;
  font-weight: 600;
  padding-top: 0.25rem;
  border-top: 1px solid var(--border);
}

.advanced input {
  width: 4.5rem;
  font: inherit;
  padding: 0.4rem 0.5rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  text-align: center;
}

.hint {
  margin: 0;
  font-size: 0.8rem;
  color: var(--muted);
}

.notice {
  margin: 2rem 0 0;
  padding: 0.85rem 1rem;
  text-align: center;
  font-size: 0.9rem;
  color: var(--muted);
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
}

.results {
  margin-top: 2.5rem;
  flex: 1;
}

.meta {
  margin: 0 0 1rem;
  text-align: center;
  font-size: 0.9rem;
  color: var(--muted);
}

.meta strong {
  color: var(--text);
  font-weight: 600;
}

.outcomes {
  display: grid;
  gap: 0.75rem;
}

@media (min-width: 520px) {
  .outcomes {
    grid-template-columns: repeat(3, 1fr);
  }
}

.outcome {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 1.25rem 1rem;
  text-align: center;
  box-shadow: var(--shadow);
}

.outcome h2 {
  margin: 0;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.outcome .delta {
  margin: 0.4rem 0 0.15rem;
  font-size: 2rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.1;
}

.outcome .new-rating {
  margin: 0;
  font-size: 0.85rem;
  color: var(--muted);
}

.outcome.gain .delta {
  color: var(--gain);
}

.outcome.loss .delta {
  color: var(--loss);
}

@media (max-width: 420px) {
  .matchup {
    grid-template-columns: 1fr auto 1fr;
    gap: 0.5rem;
  }

  .swap-btn {
    width: 2.25rem;
    height: 2.25rem;
    font-size: 1rem;
    margin-bottom: 0.5rem;
  }

  .rating-field input {
    font-size: 1.65rem;
    padding: 0.85rem 0.35rem;
  }
}